3-Phenylaminothiophen-4-carboxylic acids, to which good antiphlogistic and antipyretic properties are attributed, are described in German Patent Specification No. 1,493,705. (*) The antiphlogistic action of the 2,3-dimethylphenyl compound proved comparable to that of phenylbutazone, and its antipyretic action proved to be superior. Further interesting representatives of this class of compound are the 2,6-dichlorophenyl derivative and the 2-methyl-3-chlorophenyl derivative [Alpermann, H. G., Arzneim.-Forsch. (Drug Res.), 20 (1970) 293 and 294] and the 2-chloro-3-methylphenyl derivative [Alpermann, H. G., et al., Arzneim.-Forsch. (Drug Res.), 22 (1972) 2146 and 2147], the actions of which are superior to those of phenylbutazone. Fibrinolytic properties are also attributed to various thiophencarboxylic acids [von Kaulla, K. N., Arzneim.-Forsch., 25, 152 to 155 (1975); von Kaulla, K. N., and Thilo, D., Klin. Wochensch., 48, 668 to 673 (1970); and Thilo, D., and von Kaulla, K. N., J. Med. Chem., 13, 503 to 510 (1970)]. FNT (*) Corresponding to U.S. Pat. No. 3,445,473